Personally I like liquid cooling but both coolers are great and you cant go wrong with either. The H100 will of course give the best temps and give you more overclocking headroom especially if your wanting to go 4.5 or higher.
If you're looking at the H100i, I'd also consider a 240/280 watercooling kit. There probably isn't much difference in price, and you'll get a longer lasting, more effective, and quieter cooling system for the money. One of our members Burty117 is eyeing one at the moment (the Alphacool NexXxos kit), and there are a few outlets that ship internationally relatively cheaply (Xoxide ( I tossed in a good XSPC kit for an example), Performance PCs, Sidewinder, SpecialTech, maybe Frozen CPU )
To give you an idea of what kind of temps you can expect, add 5-15C (depending on fan speed and/or push or push-pull) to what I get with a 360 (which is about 18C over ambient). Overclocking doesn't add too much to the burden unless you're whacking up the vCore (1.4V and higher)
Tippit for the H100i it will be able to reduce your temps a bit, but for the cost of it compared to what you have now, I wouldn't consider it, the NH-D14 should be the preferred option unless you hate dust build up. Also with overclocking I can safely stay at 4.5 but considering that I had to fork out £100 to enable me to get to 4.5 from 4.2 I could hit anyway, well...